In the past papers, some of the inventory models always assume the inventory systems are one-echelon.But in the real world the inventory systems are two-echelon.

• 摘要过去的存货理论相关文献中，有些存货模式假设存货供需系统是单阶层的，但是在实际的存货供需系统中，许多情况都是二阶层的。